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In this paper, we loosen the zero equation of state of dark matter to a constant w₃₌. By using the currently available cosmic observations, which include the type-Ia supernovae, the baryon acoustic oscillation, the WiggleZ measurements of matter power spectrum, and the cosmic microwave background radiation from the firs release of Planck data through the Markov chain Monte Carlo method, we found the equation of state of dark matter in 3 regions: w₃₌=0. 000707-₀. ₀₀₀₇₄₇-₀. ₀₀₁₄₉-₀. ₀₀₁₉₆^+0. 000746+0. 00146+0. 00193. The difference between the minimum of ^2 between the and models is ₌₈₍^2=0. 446 for one extra model parameter w₃₌. Although the currently available cosmic observations favor the mildly, no significant deviation from the model is found in 1 regions.
Xu et al. (Tue,) studied this question.